Method for fabricating laminated silicon gate electrode

ABSTRACT

Within a method for forming a silicon layer, there is employed at least one sub-layer formed of a higher crystalline silicon material and at least one sub-layer formed of a lower crystalline silicon material. The lower crystalline silicon material is formed employing a hydrogen treatment of the higher crystalline silicon material. The method is particularly useful for forming polysilicon based gate electrodes with enhanced dimensional control and enhanced performance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods for fabricatingmicroelectronic fabrications. More particularly, the present inventionrelates to methods for fabricating gate electrodes within field effectdevices within semiconductor integrated circuit microelectronicfabrications.

2. Description of the Related Art

Essential in the art of semiconductor integrated circuit microelectronicfabrication is the fabrication and use of field effect devices, such asfield effect transistor (FET) devices. Field effect devices generallyemploy a gate electrode separated from a semiconductor substrate by agate dielectric layer, to thus form a conductor/insulator/semiconductorcapacitor, where charge carrier species concentrations are modulatedwithin a channel region of the semiconductor substrate incident chargeinjection into the gate electrode.

While gate electrodes are thus desirable in the art of integratedcircuit fabrication and often essential in the art of integrated circuitfabrication, gate electrodes are nonetheless not entirely withoutproblems in the art of integrated circuit fabrication. In that regard,it is often difficult in the art of integrated circuit fabrication tofabricate gate electrodes with enhanced dimensional control and enhancedperformance.

It is thus desirable in the art of integrated circuit fabrication tofabricate gate electrodes with enhanced dimensional control and enhancedperformance.

It is towards the foregoing object that the present invention isdirected.

Various gate electrode structures having desirable properties, andmethods for fabrication thereof, have been disclosed in the art ofintegrated circuit fabrication.

Included among the gate electrode structures and methods for fabricationthereof, but not limited among the gate electrode structures and methodsfor fabrication thereof, are gate electrode structures and methods forfabrication thereof disclosed within: (1) Wu, in U.S. Pat. No. 5,710,454(a stacked amorphous silicon layer method for forming a tungstensilicide polycide gate electrode); (2) Kimizuka, in U.S. Pat. No.6,013,577 (an amorphizing ion implant method for forming a polysilicongate electrode with an amorphous silicon surface; (3) Yu et al., in U.S.Pat. No. 6,162,716 (a multi-layer amorphous silicon gate electrode withmis-matched grain boundaries); and (4) Choi et al., in U.S. Pat. No.6,188,104 (a trench field effect transistor (FET) device having formedtherein a laminated amorphous silicon/polysilicon gate electrode). Thedisclosures of each of the foregoing references are incorporated hereinfully by reference.

Desirable in the art of integrated circuit fabrication are additionalmethods and materials for forming, with enhanced dimensional control andenhanced performance, gate electrodes within integrated circuit devices.

It is towards the foregoing object that the present invention isdirected.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a method forforming a gate electrode for use within an integrated circuit device.

A second object of the present invention is to provide a method inaccord with the first object of the present invention, wherein the gateelectrode is formed with enhanced dimensional control and enhancedperformance.

In accord with the objects of the present invention, there is provided amethod for forming a silicon layer.

To practice the method of the present invention, there is first provideda substrate. There is then formed over the substrate a silicon layer,wherein the silicon layer comprises at least one sub-layer formed of ahigher crystalline silicon material and at least one sub-layer formed ofa lower crystalline silicon material. Within the present invention, thelower crystalline silicon material is formed incident to a hydrogencontaining material treatment of the higher crystalline siliconmaterial.

The present invention provides a method for forming a gate electrode foruse within an integrated circuit, wherein the gate electrode is formedwith enhanced dimensional control and enhanced performance.

The present invention realizes the foregoing objects within the contextof forming a silicon layer over a substrate, wherein the silicon layermay be employed for forming a gate electrode within an integratedcircuit device. Within the present invention, the silicon layercomprises at least one sub-layer formed of a higher crystalline siliconmaterial and at least one sub-layer formed of a lower crystallinesilicon material. In addition, within the present invention, the lowercrystalline silicon material is formed incident to a hydrogen containingmaterial treatment of the higher crystalline silicon material. Byemploying within the context of the present the lower crystallinesilicon material as at least either an upper layer or a lower layerwithin a gate electrode, the gate electrode is formed with enhanceddimensional control and enhanced performance within a microelectronicfabrication, since the lower crystalline silicon material provides asmoother surface with enhanced electrical properties.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention areunderstood within the context of the Description of the PreferredEmbodiment, as set forth below. The Description of the PreferredEmbodiment is understood within the context of the accompanyingdrawings, which form a material part of this disclosure, wherein:

FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5 and FIG. 6 show a series ofschematic cross-sectional diagrams illustrating the results ofprogressive stages of fabricating, in accord with a preferred embodimentof the present invention, a gate electrode for use within a field effecttransistor (FET) device within a semiconductor integrated circuitmicroelectronic fabrication.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a method for forming a gate electrode foruse within an integrated circuit, wherein the gate electrode is formedwith enhanced dimensional control and enhanced performance.

The present invention realizes the foregoing objects within the contextof forming a silicon layer over a substrate, wherein the silicon layermay be employed for forming a gate electrode within an integratedcircuit device. Within the present invention, the silicon layercomprises at least one sub-layer formed of a higher crystalline siliconmaterial and at least one sub-layer formed of a lower crystallinesilicon material. In addition, within the present invention, the lowercrystalline silicon material is formed incident to a hydrogen containingmaterial treatment of the higher crystalline silicon material. Byemploying within the context of the present the lower crystallinesilicon material as at least either an upper layer or a lower layerwithin a gate electrode, the gate electrode is formed with enhanceddimensional control and enhanced performance within a microelectronicfabrication, since the lower crystalline silicon material provides asmoother surface with enhanced electrical properties.

While the preferred embodiment of the present invention illustrates theinvention most particularly within the context of forming a polysiliconbased gate electrode for use within a field effect transistor (FET)device within a semiconductor integrated circuit microelectronicfabrication, the present invention is not intended to be so limited.Rather, the present invention may be employed for forming siliconlayers, and in particular polysilicon layers, within variousapplications where surface smoothness and enhanced electrical propertiesare desired. Such polysilicon layers with enhanced surface smoothnessmay be employed as layers other than gate electrodes, such as forexample patterned conductor interconnect layers, within microelectronicfabrications which need not necessarily include field effect devices.Such microelectronic fabrications may include, but are not limited tointegrated circuit microelectronic fabrications, ceramic substratemicroelectronic fabrications and optoelectronic microelectronicfabrications. Within the context of forming a silicon layer in accordwith the present invention as a gate electrode within a field effectdevice, such as a field effect transistor (FET) device, the gateelectrode may be employed within field effect devices including but notlimited to planar field effect devices and trench field effect devices.

Referring now to FIG. 1 to FIG. 6, there is shown a series of schematiccross-sectional diagrams illustrating the results of progressive stagesof fabricating, in accord with a preferred embodiment of the presentinvention, a gate electrode for use within a field effect transistor(FET) device within a semiconductor integrated circuit microelectronicfabrication.

Shown in FIG. 1 is a schematic cross-sectional diagram of thesemiconductor integrated circuit microelectronic fabrication at an earlystage of its fabrication in accord with the preferred embodiment of thepresent invention.

Shown in FIG. 1, in a fist instance, is a semiconductor substrate 10having formed therein a pair of isolation regions 12 a and 12 b whichdefine an active region of the semiconductor substrate 10. In turn, asis also illustrated within FIG. 1, the active region of thesemiconductor substrate 10 has formed thereupon a gate dielectric layer14.

Within the preferred embodiment of the present invention, thesemiconductor substrate 10 may be selected from the group including butnot limited to silicon semiconductor substrates, germanium semiconductorsubstrates and silicon-germanium alloy semiconductor substrates.

Within the preferred embodiment of the present invention, the pair ofisolation regions 12 a and 12 b may be formed employing methods andmaterials as are conventional in the art of microelectronic fabrication,to form the pair of isolation regions 12 a and 12 b as isolation regionsincluding but not limited to shallow trench isolation (STI) regions andlocal oxidation of silicon (LOCOS) isolation regions.

Within the preferred embodiment of the present invention, the gatedielectric layer 14 is typically and preferably formed incident tothermal oxidation of the semiconductor substrate 10 to form the gatedielectric layer 14 of thickness from about 17 to about 35 angstroms.

Referring now to FIG. 2, there is shown a schematic cross-sectionaldiagram illustrating the results of further processing of thesemiconductor integrated circuit microelectronic fabrication whoseschematic cross-sectional diagram is illustrated in FIG. 1.

As is illustrated in FIG. 2, there is formed upon the pair of isolationregions 12 a and 12 b and the gate dielectric layer 14 a blanket firstsilicon layer 16. Within the preferred embodiment of the presentinvention, the blanket first silicon layer 16 is formed of a polysiliconmaterial, typically and preferably formed employing a chemical vapordeposition (CVD) method employing a silicon source material such as butnot limited to silane or disilane.

Typically and preferably, the chemical vapor deposition (CVD) methodalso employs: (1) a reactor chamber pressure of from about 200 to about300 torr; (2) a semiconductor substrate 10 temperature of from about 600to about 660 degrees centigrade; (3) a 5 to about 50 volume percentsilicon source material in hydrogen or helium carrier gas at anaggregate flow rate of from about 1000 to about 4000 standard cubiccentimeters per minute (sccm). Typically and preferably, the blanketfirst silicon layer 16 is formed to a thickness of from about 200 toabout 1000 angstroms.

Referring now to FIG. 3, there is shown a schematic cross-sectionaldiagram illustrating the results of further processing of thesemiconductor integrated circuit microelectronic fabrication whoseschematic cross-sectional diagram is illustrated in FIG. 2.

As is illustrated within FIG. 3, the blanket first silicon layer 16which is formed of the polysilicon material is treated with a firsthydrogen treatment 18 to form therefrom a hydrogen treated blanket firstsilicon layer 16′.

Within the present invention, such a hydrogen treatment of a siliconlayer formed of a polysilicon material to form therefrom a hydrogentreated silicon layer causes for a reduction of crystallinity of thepolysilicon material. The reduction of crystallinity of the polysiliconmaterial provides a partial polysilicon material comprising at least inpart an amorphous silicon material.

Within the present invention, the first hydrogen treatment 18 may beeffected employing a hydrogen treatment selected from the groupincluding but not limited to hydrogen thermal annealing treatments andhydrogen containing plasma treatments.

When employing a hydrogen thermal annealing treatment for the firsthydrogen treatment 18 when forming from the blanket first silicon layer16 the hydrogen treated blanket first silicon layer 16′, the hydrogenthermal annealing treatment employs: (1) a semiconductor substrate 10and blanket first silicon layer 16 temperature of from about 600 toabout 660 degrees centigrade; (2) a hydrogen containing material (suchas hydrogen or hydrazine) flow rate of from about 500 to about 5000standard cubic centimeters per minute (sccm); and (3) a hydrogentreatment time of from about 1 to about 3 minutes.

When employing a hydrogen containing plasma treatment for the firsthydrogen treatment 18 when forming from the blanket first silicon layer18 the hydrogen treated blanket first silicon layer 16′, the hydrogencontaining plasma employs: (1) a reactor chamber pressure of from about200 to about 300 torr; and (2) a semiconductor substrate 10 and blanketfirst silicon layer 16 temperature of from about 600 to about 660degrees centigrade.

Within the context of either of the two foregoing hydrogen treatments,there is provided a reduction of crystallinity of the blanket firstsilicon layer 16 when formed of a polysilicon material typically acolumnar polysilicon material. Typically and preferably, the hydrogentreated blanket first silicon layer 16′ has a crystallinity of fromabout 5 to about 50 percent of the blanket first silicon layer 16. Amore severe hydrogen treatment may provide a more complete reduction ofcrystallinity to yield a completely amorphous silicon material for thehydrogen treated blanket first silicon layer 16′, but such is typicallynot preferred within the present invention.

Referring now to FIG. 4, there is shown a schematic cross-sectionaldiagram illustrating the results of further processing of thesemiconductor integrated circuit microelectronic fabrication whoseschematic cross-sectional diagram is illustrated in FIG. 3.

Shown in FIG. 4 is the results of forming upon the hydrogen treatedblanket first silicon layer 16′ a blanket second silicon layer 20.

Within the preferred embodiment of the present invention, the blanketsecond silicon layer 20 may be formed employing methods and materialsanalogous or equivalent to the methods and materials employed forforming the blanket first silicon layer 16 as illustrated within theschematic cross-sectional diagram of FIG. 2. Typically and preferably,the blanket second silicon layer 20 is formed to a thickness of fromabout 200 to about 1000 angstroms.

Referring now to FIG. 5, there is shown a schematic cross-sectionaldiagram illustrating the results of further processing of themicroelectronic fabrication whose schematic cross-sectional diagram isillustrated in FIG. 4.

As is illustrated within the schematic cross-sectional diagram of FIG.5, the blanket second silicon layer 20 has been treated with a secondhydrogen treatment 22 to form therefrom a hydrogen treated blanketsecond silicon layer 20′ comprising a blanket hydrogen untreated secondsilicon sub-layer 20″ and a blanket hydrogen treated second siliconsub-layer 20′″.

Within the preferred embodiment of the present invention, the secondhydrogen treatment 22 is otherwise generally analogous or equivalent tothe first hydrogen treatment 18 as illustrated within the schematiccross-sectional diagram of FIG. 3, but since the blanket second siliconlayer 20 is formed to a greater thickness than the blanket first siliconlayer 16, the hydrogen treated blanket second silicon sub-layer 20′″ ofthe hydrogen treated blanket second silicon layer 20′ is not formed forthe entire thickness of the blanket second silicon layer 20. Typicallyand preferably, the hydrogen untreated blanket second silicon sub-layer20″ is formed to a thickness of from about 200 to about 1000 angstromsand the hydrogen treated blanket second silicon sub-layer 20′″ is formedto a thickness of from about 200 to about 1000 angstroms.

Referring now to FIG. 6, there is shown a schematic cross-sectionaldiagram illustrating the results of further processing of thesemiconductor integrated circuit microelectronic fabrication whoseschematic cross-sectional diagram is illustrated in FIG. 5.

As is illustrated in FIG. 6, the hydrogen treated blanket second siliconlayer 20′ and the hydrogen treated blanket first silicon layer 16′ havebeen patterned to form a hydrogen treated patterned second silicon layer20 a′ (comprising a hydrogen untreated patterned second siliconsub-layer 20 a″ and a hydrogen treated patterned second siliconsub-layer 20 a′″) and a corresponding hydrogen treated patterned firstsilicon layer 16 a′, where the aggregate of the foregoing patternedlayers forms a composite silicon layer as a gate electrode 24 within afield effect transistor (FET) device within the semiconductor integratedcircuit microelectronic fabrication whose schematic cross-sectionaldiagram is illustrated in FIG. 6.

Also illustrated within the schematic cross-sectional diagram of FIG. 6,and also comprising the field effect transistor (FET) device is a pairof source/drain regions 26 a and 26 b formed into the active region ofthe semiconductor substrate 10 at locations not covered by the gateelectrode 24.

Within the preferred embodiment of the present invention, the patterningof the hydrogen treated blanket second silicon layer 20′ and thehydrogen treated blanket first silicon layer 16′ to form thecorresponding hydrogen treated patterned second silicon layer 20 a′ andthe hydrogen treated patterned first silicon layer 16 a′ may be effectedemploying methods as are conventional in the art of semiconductorintegrated circuit microelectronic fabrication. Similarly, the pair ofsource/drain regions 26 a and 26 b may also be formed employing methodsas are conventional in the art of semiconductor integrated circuitmicroelectronic fabrication.

Upon forming the semiconductor integrated circuit microelectronicfabrication whose schematic cross-sectional diagram is illustrated inFIG. 6, there is formed a semiconductor integrated circuitmicroelectronic fabrication having formed therein a field effecttransistor (FET) device in accord with the preferred embodiment of thepresent invention. Within the semiconductor integrated circuitmicroelectronic fabrication, a gate electrode within the field effecttransistor (FET) device is formed with multiple silicon layers havingdiffering crystallinity, and in particular a polysilicon middle layerhaving formed thereupon and there beneath a pair of hydrogen treatedpolysilicon layers having lesser crystallinity than the polysiliconmiddle layer.

Within the present invention, the lesser crystalline silicon layerformed beneath the middle layer of the gate electrode provides the gateelectrode with enhanced performance insofar as the lesser crystallinityprovides for smooth contact with the gate dielectric layer. Suchenhanced performance may be measured in terms of enhanced carriermobility, decreased sheet resistance and enhanced dopant diffusioninhibition. Similarly, the lesser crystalline silicon layer formed uponthe middle layer of the gate electrode provides for enhanced dimensionalcontrol when forming the gate electrode, since the reduced crystallinityprovides for a smoother surface which is more readily uniformly andprecisely patterned.

As is understood by a person skilled in the art, although the preferredembodiment of the present invention illustrates the present inventionwithin the context of a gate electrode within a field effect transistor(FET) device formed of a polysilicon middle layer laminated on both ofits top surface and bottom surface with a hydrogen material treatedsilicon layer of lesser crystallinity, the present invention alsoprovides value within the context of a gate electrode (or other siliconlayer) formed of a middle polysilicon layer having laminated to onlyeither its top or bottom a lesser crystalline silicon layer formedemploying a hydrogen treatment method.

As is understood by a person skilled in the art, the preferredembodiment of the present invention is illustrative of the presentinvention rather than limiting of the present invention. Revisions andmodifications may be made to methods, materials, structures anddimensions in accord with the preferred embodiment of the presentinvention, while still providing a semiconductor integrated circuitmicroelectronic fabrication in accord with the present invention,further in accord with the accompanying claims.

1-24. (canceled)
 25. A microelectronic structure comprising: asubstrate; and a silicon layer formed over the substrate, wherein thesilicon layer comprises at least one sub-layer formed of a highercrystalline silicon material and at least one sub-layer formed of alower crystalline silicon material, and wherein the lower crystallinesilicon material has a crystallinity of from about 70 to about 90percent of the higher crystalline silicon material.
 26. The structure ofclaim 25 wherein the silicon layer comprises a lower crystalline siliconmaterial sub-layer formed upon a higher crystalline silicon materialsub-layer.
 27. The structure of claim 25 wherein the silicon layercomprises a higher crystalline silicon material sub-layer formed upon alower crystalline silicon material sub-layer.
 28. The structure of claim25 wherein the silicon layer comprises a higher crystalline siliconmaterial sub-layer sandwiched between a pair of lower crystallinesilicon material sub-layers.
 29. The structure of claim 25 wherein thelower crystallinity silicon material is formed by treating the highercrystallinity silicon material with a hydrogen containing material.